GENEVA (Reuters) - The Iraqi government's assault to retake the city of Mosul could take months, prompting more and more civilians to try to flee to avoid being trapped between frontlines, a senior official of the International Committee of the Red Cross told Reuters.

A growing number of wounded, more than 100 on some days, are emerging from rural areas surrounding the city of one million that is held by Islamic State forces, said Dominik Stillhart, director of ICRC operations worldwide.

"What we see now on the ground is indeed that the fight in Mosul is not just going to stop anytime soon because the resistance is very strong," Stillhart, back from visiting Iraq, said in an interview on Thursday at ICRC headquarters in Geneva.

"It is likely that we will see long, drawn-out fighting with very serious suffering of a population that will once again be caught between two frontlines," he said. "It is reasonable to expect that this is going to take weeks if not months."

More than six weeks into the offensive against Islamic State's last major city stronghold in Iraq, the army is trying to dislodge militants dug in among civilians in the eastern districts, the only side Iraqi troops have been able to breach.

"The original idea of the government as they told me, government officials, is that people should stay in their houses as much as possible," Stillhart said. "But of course the longer the fighting will be drawn out, the more people will probably try to flee."

Some 70,000 people had been displaced so far, a relatively low number that he said suggested the Iraqi military was giving consideration to protecting the civilian population.

"But looking at what is happening elsewhere in the Middle East, we are of course concerned about yet another situation where we have intense urban warfare with large-scale destruction which will of course heavily impact on the civilian population."

The ICRC is focusing on providing food and shelter material to civilians who have fled Mosul, and on water and sanitation projects, Stillhart said.

SCREENING CENTERS

Iraqi officials have allowed ICRC officials to monitor the condition of those fleeing Mosul who are questioned or detained, he said. "We have free access to these screening centers, we can monitor the screening."

ICRC findings on treatment and detention conditions are confidential, as with their prison visits across Iraq.

The ICRC deploys nearly 1,000 staff in Iraq, its second largest operation worldwide after Syria. Its first full surgical team of six will start working next week in Shikhan hospital, north of Mosul, Stillhart said.

It has provided first aid training to 900 health workers and supplied hospitals with dressing kits and surgical instruments.

"But it is true, as soon as the fighting intensifies and there are big battles, that there are situations where individual hospitals will have difficulties to cope with the number of wounded," Stillhart said.

Islamic State forces are alleged to have used chemical weapons earlier this year in northern Iraq.

"We have trained and equipped our staff for possible small-scale use of chemical weapons, but we have also prepared some of these medical facilities with training and equipment to receive people affected by chemical weapons," Stillhart said.